Constraining the origin of the Martian moons through global remote sensing and sample return: the MMX mission at launch

The Martian Moons eXploration (MMX) mission, scheduled for launch in 2026, will conduct the first comprehensive exploration of the Martian moons and return samples from Phobos to Earth in 2031. The mission aims to determine the origin of Phobos and Deimos and to clarify the evolution of the Martian system as a key interface in the inner Solar System.

A major component of MMX is its global remote sensing campaign, which will characterize the composition, geology, and physical properties of the Martian moons. After arrival, the spacecraft will perform multi-year observations of Phobos and Deimos, with particular emphasis on systematic surveys of Phobos from quasi-satellite orbits. Operating at altitudes of ~10–190 km, these observations will provide near-global coverage at progressively higher spatial resolution, enabling characterization of surface heterogeneity and identification of candidate sampling sites.

The remote sensing payload includes high-resolution imaging (TENGOO), multiband visible imaging (OROCHI), near-infrared spectroscopy (MIRS), laser altimetry (LIDAR), and elemental measurements by a neutron and gamma-ray spectrometer (MEGANE). Together, these instruments will map surface morphology, mineralogy, and elemental composition, including the distribution of hydrated materials and hydrogen, which are key indicators of formation processes. In addition, the CNES/DLR-built IDEFIX rover will perform in situ investigations of the Phobos surface, characterizing regolith mechanical, thermal, and mineralogical properties through imaging, radiometry, and Raman spectroscopy, while also supporting landing site assessment for the main spacecraft.  In parallel, MMX will observe the Martian atmosphere and circum-Martian environment, linking surface processes with dust transport, volatile cycling, and atmospheric escape. These datasets will provide key constraints to distinguish between competing formation scenarios, such as primitive asteroidal capture versus formation through a giant impact involving Martian material.

Complementing the remote sensing observations, sample return from Phobos will provide ground truth for orbital observations and enable laboratory analyses at high precision, including potential access to Martian ejecta preserved in Phobos regolith. Within this framework, remote sensing plays a central role in establishing global context and guiding the interpretation of returned materials.

Through the integration of remote sensing, in situ observations, and sample analyses, MMX will deliver a comprehensive understanding of the Martian moons and the evolution of the Martian system, providing new insights into planetary formation, volatile evolution, and material transport processes in the inner Solar System.